Cogeneration apparatus are known which not only generate electric energy by driving an electric generator by means of an engine but also acquire heat energy from hot exhaust gas, discharged from the engine, to give the acquired heat energy to a water heater and/or heating appliance. One example of such cogeneration apparatus is disclosed in Japanese Patent Application Laid-Open Publication No. HEI-8-4586 (JP-A H08-004586).
FIG. 10 hereof shows the cogeneration apparatus 100 disclosed in JP-A H08-004586. The cogeneration apparatus 100 generates heat energy by driving the electric generator 102 by means of the engine 101 and acquires heat energy from high-temperature exhaust gas, discharged from the engine 101, by means of an exhaust heat exchanger 103. Further, in order to recover and use heat energy, the cogeneration apparatus 100 includes a first system 104 for circulating cooling water for the engine 101, a second system 106 comprising a hot water storage tank 105 etc., and a hot water heat exchanger 107 for effecting heat exchange between the first system 104 and the second system 106.
The cooling water not only acquires heat energy by cooling the engine 101 but also acquires heat energy from exhaust gas of the engine 101 through the exhaust heat exchanger 103, so that it takes a high temperature. The thus-heated cooling water flows to the hot water heat exchanger 107 to transfer the heat energy to a low-temperature heat medium. The heat energy thus transferred to the heat medium by means of the hot water heat exchanger 107 is transferred to a hot water consuming appliance 108 and/or heat consuming appliance 109 via the hot water storage tank 105. As noted above, the cogeneration apparatus 100 includes the discharge heat exchanger 103 and the hot water heat exchanger 107 to effect the heat transfer.
However, because the discharge heat exchanger 103 and the hot water heat exchanger 107 are both relatively great in size, the cogeneration apparatus 100 tends to have a overall great size, despite a recent demand for compactization, i.e. reduction in size, of the cogeneration apparatus 100.